Temperature fuse element, temperature fuse and battery using the same

ABSTRACT

A thermal fuse comprises: a first insulating film to which a pair of metal terminals are attached; a fusible alloy located above the first insulating film and connected between the leading end portions of the pair of metal terminals; and a second insulating film located above the fusible alloy and attached to the first insulating film so as to define a space with the first insulating film. The fusible alloy includes an Sn—Bi—In—Zn alloy containing 0.5 to 15 weight % of Bi, 45 to 55 weight % of In and 0.5 to 5 weight % of Zn with the balance being Sn.

TECHNICAL FIELD

The present invention relates to a thermal fuse element, a thermal fuseand a batter using such a thermal fuse.

BACKGROUND ART

In recent years, it has become problematic that Cd, Pb used inelectronic devices leach into the natural environment and, accordingly,there has been an increasing demand for making electronic devicesCd-free and Pb-free. Therefore, thermal fuses used to protect theelectronic devices are desired to contain neither Pb nor Cd.

Particularly, in a packaged battery used as a power supply of a mobilephone, a battery and a thermal fuse are connected by spot welding, andPb-free solder has been used even in a protecting circuit forcontrolling the charging and discharging of the battery. Thus, there hasbeen a strong demand for thermal fuses containing neither Pb nor Cd.

Since the heat capacity of the above packaged battery becomes smallerwith the miniaturization thereof, there has been an increasing tendencyto speed up a temperature rising rate during the heat generation. Thus,the thermal fuse is required to have a low operating temperature of 85to 108° C. in order to quickly shut off a current in the event ofabnormality.

In the case of using the packaged battery, for example, under thescorching sun, the packaged battery is, in some cases, used while thesurface temperature thereof is about 55° C. due to the ambienttemperature and the heat generation by the battery. Therefore, thethermal fuse is required to secure its function even in the case ofbeing used for a long time in a temperature state of about 55° C.

FIG. 7 is a section of a prior art thermal fuse. As shown in FIG. 7, theprior art thermal fuse comprises: a cylindrical insulating casing 1having openings at opposite ends; a fusible alloy 2 in the form of asubstantially round column or a substantially rectangular columnarranged in the insulating casing 1; a pair of lead conductors 3 whoseeach one end portion connected with the corresponding end of the fusiblealloy 2 and the other end portion protruded through the correspondingopening of the insulating casing 1 to the outside of the insulatingcasing 1; flux (not shown) coated on the fusible alloy 2; and sealingelements 4 sealing the openings at the opposite end portions of theinsulating casing 1.

For example, in a thermal fuse operable at 85 to 108° C., the fusiblealloy 2 has been made of an Sn—Cd—In eutectic alloy (melting point of93° C.) or an Sn—Bi—Pb eutectic alloy (melting point of 95° C.). Analloy-type thermal fuse disclosed in Japanese Unexamined PatentPublication No. 2000-90792 is known as such a prior art thermal fuse.

However, since the prior art thermal fuse comprises the fusible alloy 2containing Pb or Cd, there is a possibility of disturbing the naturalenvironment due to the leached Pb or Cd if electronic devices using thisthermal fuse are discarded.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a thermal fuse element,a thermal fuse and a battery using such a thermal fuse, which aredesigned to suppress harm to the natural environment.

One aspect of the present invention is directed to a thermal fuseelement which is cut off by melting at a specified temperature,including either an Sn—Bi—In—Zn alloy or an Sn—In—Zn alloy.

Since this thermal fuse element includes either an Sn—Bi—In—Zn alloy oran Sn—In—Zn alloy, neither Pb nor Cd is contained in the thermal fuseelement unlike the prior art. Thus, it is possible to provide a thermalfuse element capable of suppressing harm to the natural environment.

The thermal fuse element preferably includes an Sn—Bi—In—Zn alloycontaining: 0.5 to 15 weight % of Bi; 45 to 55 weight % of In; and 0.5to 5 weight % of Zn; with the balance being Sn. In this case, it ispossible to provide a thermal fuse element having an arbitrary operatingtemperature of 85° C. to 107° C.

The thermal fuse element more preferably includes an Sn—Bi—In—Zn alloycontaining: 0.5 to 15 weight % of Bi; 48 to 55 weight % of In; 1.3 to 5weight % of Zn; with the balance being Sn.

In this case, the thermal fuse element can be used for a long time at atemperature exceeding the melting point of flux, and the fluctuation ofthe melting point caused by the composition variation can be reduced.Thus, it is possible to provide a thermal fuse element having a highlyprecise cut-off temperature by melting.

The thermal fuse element may include an Sn—In—Zn alloy containing: 45 to55 weight % of In; and 0.5 to 5 weight % of Zn; with the balance beingSn.

In this case, the melting point of the Sn—In—Zn alloy is about 107° C.and a difference between a solidus temperature and a liquidustemperature becomes smaller to reduce a temperature range of asolid-liquid mixture. Thus, it is possible to provide a thermal fuseelement having a small operating temperature variation at about 107° C.

The thermal fuse element more preferably includes an Sn—In—Zn alloycontaining: 48 to 55 weight % of In; and 1.3 to 5 weight % of Zn; withthe balance being Sn.

In this case, the thermal fuse element can be used for a long time at atemperature exceeding the melting point of the flux, and the fluctuationof the melting point caused by the composition variation can be reduced.Thus, it is possible to provide a thermal fuse element having a highlyprecise cut-off temperature by melting.

Another aspect of the present invention is directed to a thermal fusecomprising a fusible alloy cut off by melting at a specifiedtemperature, wherein the fusible alloy includes either an Sn—Bi—In—Znalloy or an Sn—In—Zn alloy.

Since the fusible alloy includes either an Sn—Bi—In—Zn alloy or anSn—In—Zn alloy in this thermal fuse, neither Pb nor Cd is contained inthe fusible alloy unlike the prior art. Thus, it is possible to providea thermal fuse capable of suppressing harm to the natural environment.

The fusible alloy preferably includes an Sn—Bi—In—Zn alloy containing:0.5 to 15 weight % of Bi; 45 to 55 weight % of In; and 0.5 to 5 weight %of Zn; with the balance being Sn. In this case, it is possible toprovide a thermal fuse element having an arbitrary operating temperatureof 85° C. to 107° C.

The fusible alloy more preferably includes an Sn—Bi—In—Zn alloycontaining: 0.5 to 15 weight % of Bi; 48 to 55 weight % of In; and 1.3to 5 weight % of Zn; with the balance being Sn.

In this case, the thermal fuse can be used for a long time at atemperature exceeding the melting point of the flux, and the fluctuationof the melting point caused by the composition variation can be reduced.Thus, it is possible to provide a thermal fuse having a highly precisecut-off temperature by melting.

The fusible alloy may include an Sn—In—Zn alloy containing: 45 to 55weight % of In; and 0.5 to 5 weight % of Zn; with the balance being Sn.

In this case, the melting point of the Sn—In—Zn alloy is about 107° C.and a difference between a solidus temperature and a liquidustemperature becomes smaller to reduce a temperature range of asolid-liquid mixture. Thus, it is possible to provide a thermal fuseelement having a small operating temperature variation at about 107° C.

The fusible alloy may include an Sn—In—Zn alloy containing: 48 to 55weight % of In; 1.3 to 5 weight % of Zn; with the balance being Sn.

In this case, the thermal fuse can be used for a long time at atemperature exceeding the melting point of the flux, and the fluctuationof the melting point caused by the composition variation can be reduced.Thus, it is possible to provide a thermal fuse having a highly precisecut-off temperature by melting.

Preferably, the fusible alloy is coated by flux and the melting point ofthe flux is 60° C. or higher.

In this case, even if the thermal fuse is used for a long time at about55° C., a decrease of an activator contained in the flux can be madesmaller. As a result, it is possible to provide a thermal fuse whosequick cut-off ability by melting can be ensured for a long time.

Preferably, the fusible alloy is coated by flux and a bromide activatoris added in the flux.

In this case, even if the thermal fuse is used for a long time at atemperature exceeding the melting point of the flux, a decrease of theactivator contained in the flux can be reduced. As a result, it ispossible to provide a thermal fuse whose quick cut-off ability bymelting can be ensured for a long time.

The thermal fuse preferably further comprises: a pair of metalterminals; a first insulating film to which the pair of metal terminalsare attached; and a second insulating film attached to the firstinsulating film so as to define a space with the first insulating films;wherein the fusible alloy is arranged between the first and secondinsulating films and connected between the leading end portions of thepair of metal terminals.

In this case, it is possible to cover the fusible alloy by the first andsecond insulating films, to seal the fusible alloy by sealably fixing anouter peripheral portion of the insulating film and that of the secondinsulating film while leaving a portion where the fusible alloy isprovided unfixed. Thus, the deterioration of the fusible alloy can beprevented.

La is preferably set to lie within a range of 2.0 mm to 7.5 mm, whereinthe La is a length of a thermal-fuse main portion comprising the firstinsulating film, the second insulating film and the fusible alloy. Inthis case, the thermal fuse can be miniaturized.

Lb is preferably set to lie within a range of 0.4 mm to 1.5 mm, whereinthe Lb is a thickness between the outer surface of the first insulatingfilm and the outer surface of the second insulating film. In this case,the thermal fuse can be thinned.

Preferably, a projection is formed at an end portion of each metalterminal, the pair of metal terminals are attached to the firstinsulating film such that the projections project from the firstinsulating film side toward the second insulating film side, and thefusible alloy is connected with the projections. In this case, the pairof metal terminals can be precisely attached to the first insulatingfilm, and the thin-type thermal fuse can be produced with highprecision.

A projection is preferably formed at an end portion of each metalterminal which extends out from the first insulating film and from thesecond insulating film. In this case, if the metal terminals andexternal wiring are connected at the projections by electric welding, awelding current can be concentrated. Thus, welding strength and weldingpositions can be stabilized, thereby improving productivity.

The thermal fuse may further comprise: an insulating casing in a form ofa tube having a bottom formed and having an opening; a pair of leadconductors whose each one end portion protruded in the same directionthrough the opening of the insulation casing outside the insulatingcasing; and a sealing element for sealing the opening of the insulatingcasing; wherein the fusible alloy is placed in the insulating casing andconnected with the other end portions of the pair of lead conductors.

In this case, the pair of lead conductors whose the other end portionsare connected with the fusible alloy protrudes the one end portions inthe same direction through the opening of the insulating casing to theoutside of the insulating casing. Thus, a degree of freedom in mountingthis thermal fuse on a battery or the like can be improved.

The thermal fuse may further comprise: an insulating casing in a form ofa cylindrical tube having openings at opposite ends; a pair of leadconductors whose each one end portion protruded through thecorresponding one of the openings at the opposite ends of the insulatingcasing; and sealing elements for sealing the openings at the oppositeends of the insulating casing; wherein the fusible alloy is placed inthe insulating casing and connected with the other ends of the pair oflead conductors.

In this case, since the insulating casing having the fusible alloyplaced therein is in a form of a cylindrical tube having openings at theopposite ends, there is no directionality upon mounting the thermal fuseon a battery or the like, wherefore the thermal fuse can be easilyhandled at the time of production.

Still another aspect of the present invention is directed to a battery,comprising: a battery main body; and a thermal fuse electricallyconnected to shut off a current upon an abnormal heat generation of thebattery main body, wherein the thermal fuse includes a fusible alloywhich is cut off by melting at a specified temperature, and the fusiblealloy includes either an Sn—Bi—In—Zn alloy or an Sn—In—Zn alloy.

In this battery, neither Pb nor Cd is contained in the fusible alloy ofthe thermal fuse unlike the prior art. Thus, it is possible to provide abattery capable of suppressing harm to the natural environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top view of a thin-type thermal fuse according to a firstembodiment of the invention,

FIG. 1B is a section along I-I of FIG. 1A, and

FIG. 1C is a top view partly in section corresponding to FIG. 1A.

FIG. 2A is a top view of a thin-type thermal fuse according a secondembodiment of the invention, and

FIG. 2B is a section along II-II of FIG. 2A.

FIG. 3A is a top view of a thin-type thermal fuse according to a thirdembodiment of the invention,

FIG. 3B is a section along III-III of FIG. 3A, and

FIG. 3C is a top view partly in section corresponding to FIG. 3A.

FIG. 4 is a perspective view of a battery using the inventive thin-typethermal fuse.

FIG. 5 is a section of a radial-type thermal fuse according to a fourthembodiment of the invention.

FIG. 6 is a section of an axial-type thermal fuse according to a fifthembodiment of the invention.

FIG. 7 is a section of a prior art thermal fuse.

BEST MODES OF CARRYING OUT THE INVENTION First Embodiment

FIGS. 1A to 1C are views showing the construction of a thin-type thermalfuse according to a first embodiment of the invention, wherein FIG. 1Ais a top view, FIG. 1B is a section along I-I of FIG. 1A, and FIG. 1C isa top view partly in section corresponding to FIG. 1A.

As shown in FIGS. 1A and 1B, the thin-type thermal fuse comprises: apair of metal terminals 12; a first insulating film 11 to which the pairof metal terminals 12 are attached; a second insulating film 14 attachedto the first insulating film 11 in such a manner as to define a spacewith the first insulating film 11; and a fusible alloy 13 arrangedbetween the first and second insulating films 11, 14 and connectedbetween the leading end portions of the pair of metal terminals 12.

The insulating film 11 is a sheet-like insulating film having amonolayer structure, and the pair of metal terminals 12 narrower thanthe first insulating film 11 are attached to the first insulating film11. The fusible alloy 13 forms a thermal fuse element and bridges theleading end portions of the metal terminals 12 in the middle of theupper surface of the first insulating film 11, thereby being locatedabove the first insulating film 11 to connect the leading end portionsof the metal terminals 12.

Flux (not shown) including a resin obtained by adding a wax componentcontaining amide stearate and the like and by adding an activator torosin is coated around the fusible alloy 13. The second insulating film14 is a sheet-like insulating film having a monolayer structure, locatedabove the fusible alloy 13, and so sealed to the-first insulating film11 as to define an inner space with the first insulating film 11.

In this way, the fist and second insulating films 11, 14 enclose thefusible alloy 13, and the outer peripheral portion of the firstinsulating film 11 and that of the second insulating film 14 are sealedand fixed to each other while leaving a portion where the fusible alloy13 is provided unfixed, thereby sealing the fusible alloy 13 to preventthe deterioration of the fusible alloy 13.

The thicknesses of the first and second insulating films 11, 14 arepreferably 0.15 mm or smaller. If the thickness exceeds 0.15 mm, thethickness of the thermal fuse itself becomes thick, which is unsuitablefor the thin-type thermal fuse.

Specific materials for the first and second insulating films 11, 14 maybe a resin (preferably thermoplastic resin) containing any one of PET(polyethylene terephthalates), PEN (polyethylene naphthalates), ABSresin, SAN resin, polysulfone resin, polycarbonate resin, noryl, vinylchloride resin, polyethylene resin, polyester resin, polypropyleneresin, polyamide resin, PPS resin, polyacetal, fluororesin andpolyesters as a main component.

Although the first and second insulating films 11, 14 have monolayerstructures in this embodiment, the present invention is not particularlylimited thereto. Sheets made of different materials may be laminated.For example, if the first and second insulating films 11, 14 are made ofa film obtained by laminating a PET (polyethylene terephthalate) filmand a PEN (polyethylene naphthalate) film, the strengths thereof can beincreased, whereby mechanical strength can be improved. Further, in thecase of fabricating the first and second insulating films 14 to havemultilayer structures, a combination of a material having a low heatresistance and the one having a high heat resistance can be used inaddition to the above combination of the materials.

If La denotes the length of a thermal-fuse main portion including thefirst and second insulating films 11, 14 and the fusible alloy 13, i.e.the length of the longer sides of the first and second insulating films11, 14, a sufficient insulation distance cannot be ensured after cut offby melting in the case that La is below 2.0. On the other hand, in thecase that La exceeds 7.5 mm, a necessary installation area increases ifthe thin-type thermal fuse is installed in a small-size battery. Thus,this is not practical. Accordingly, the length La of the thermal-fusemain portion is preferably 2.0 mm to 7.5 mm.

If Lb denotes the thickness from the outer surface of the firstinsulating film 11 to the outer surface of the second insulating film14, i.e. the thickness from the lower surface of the first insulatingfilm 11 to the upper surface of the second insulating film 14, asufficient space for accommodating the fusible alloy 13 cannot beensured in the case that Lb is below 0.4 mm. On the other hand, in thecase that Lb exceeds 1.5 mm, the thickness of the thin-type thermal fusebecomes too thick in relation to projections, e.g. those of electrodesof the battery in which the thin-type thermal fuse is used, and thishinders the miniaturization of the battery. Accordingly, the thicknessLb from the lower surface of the first insulating film 11 to the uppersurface of the second insulating film 14 is preferably 0.4 mm to 1.5 mm.

The pair of metal terminals 12 are strip-shaped or wire-shaped andmainly including for example nickel metal, nickel alloy like a coppernickel alloy, nickel or nickel alloy added with the other element(s),and the like. For instance, if the metal terminals 12 include a materialwhose nickel content is 98% or higher, its electrical resistivity is aslow as 6.8×10⁻⁸ Ω·m to 12×10⁻⁸Ω·m. Thus, reliability such as corrosionresistance can be astonishingly improved.

The thickness of the metal terminals 12 themselves is preferably 0.15 mmor smaller. This is because the thermal fuse becomes too thick andunsuitable for a thin-type thermal fuse if the thickness exceeds 0.15mm.

The metal terminals 12 are preferably made of a material having Young'smodulus of 3×10¹⁰ Pa to 8×10¹⁰ Pa and a tensile strength of 4×10⁸ Pa to6×10⁸ Pa. In this case, there is no likelihood of inadvertently bendingthe metal terminals 12 during handling or transportation, it is easy tobend the terminals and occurrences of breakage and other undesirableevent can be prevented during bending.

More specifically, if Young's modulus of the metal terminals 12 is below3×10¹⁰ Pa, it is too easy to bend the metal terminals 12 and,accordingly, portions (e.g. electrically connecting portions at the endportions of the metal terminals 12) of the metal terminals 12 whichshould not be bent are likely to become uneven, thereby causing aproblem of making it difficult to electrically connect the metalterminals 12 with the fusible alloy 13 by welding. On the other hand, ifYoung's modulus exceeds 8×10¹⁰ Pa, portions of the metal terminalsdesired to be bent are difficult to bend, or broken. Further, if thetensile strength of the metal terminals 12 is below 4×10⁸ Pa, it is tooeasy to bend the metal terminals 12. On the other hand, if the tensilestrength exceeds 6×10⁸ Pa, portions of the metal terminals 12 desired tobe bent are difficult to bend, or broken.

The fusible alloy 13 can be produced by squeezing the wire-shapedfusible alloy having a circular cross section into a wire having athickness of 0.4 mm or smaller and a rectangular or elliptical crosssection and cutting the resulting wire to a suitable length. Diedrawing, die extrusion or the like can be used as a method for producingthe fusible alloy 13 into the wire. Further, the metal terminals 12 andthe fusible alloy 13 can be connected by laser welding, heat welding,ultrasonic welding or the like. Particularly in the case of using laserwelding, the fusible alloy 13 can be connected without damaging itsunwelded portions since a heat-generating portion can be made smaller.

The fusible alloy 13 includes an Sn—In—Zn alloy or an Sn—Bi—In—Zn alloy.In this case, a thin-type thermal fuse having an operating temperatureof 108° C. or lower can be provided.

The fusible alloy 13 preferably includes an Sn—In—Zn alloy containing:45 to 55 weight % of In; and 0.5 to 5.0 weight % of Zn; with the balancebeing Sn. In such a case, the melting point of the Sn—In—Zn alloy isabout 107° C., and a difference between a solidus temperature and aliquidus temperature becomes smaller to reduce a temperature range of asolid-liquid mixture. Thus, it is possible to provide a thin-typethermal fuse having a small operating temperature variation at about107° C.

Since the melting point can be decreased by adding Bi to the aboveSn—In—Zn alloy and reducing the content of Sn, the fusible alloy 13 mayinclude an Sn—Bi—In—Zn alloy containing: 0.5 to 15 weight % of Bi; 45 to55 weight % of In; and 0.5 to 5.0 weight % of Zn; with the balance beingSn. In such a case, it is possible to provide a thin-type thermal fusehaving an arbitrary operating temperature of 85° C. to 107° C.Specifically, if the content of Bi exceeds 15 weight %, the meltingpoint falls below 85° C. and the difference between the solidustemperature and the liquidus temperature becomes larger to increase anoperating temperature variation, wherefore a practical thin-type thermalfuse cannot be provided.

If the content of Zn exceeds 5.0 weight % in the above Sn—In—Zn alloy orSn—Bi—In—Zn alloy, the viscosity of the melted fusible alloy 13increases. Thus, a time required for the fusible alloy 13 to be cut offafter being melted is likely to vary. Therefore, the composition ratioof Zn is preferably 5.0 weight % or smaller.

In the case that the flux coated on the fusible alloy 13 is melted, thecomposition ratios of In and Zn may decrease since, out of the metalsconstituting the fusible alloy 13, In and Zn have a higher reactivitywith the flux than other metals. Thus, in the case of using the thermalfuse at a temperature exceeding the melting point of the flux for a longtime, it is necessary to set high composition ratios for these metals.Therefore, in the above Sn—In—Zn alloy or Sn—Bi—In—Zn alloy, it ispreferable to set the content of In to 48 to 55 weight % and that of Znto 1.3 to 5.0 weight %.

Further, if the composition ratio of Zn is 1.3 to 5.0 weight % in theabove Sn—In—Zn alloy or Sn—Bi—In—Zn alloy, the melting point becomesquite stable for the composition ratio of Zn. Thus, if the compositionratio of Zn is 1.3 to 5.0 weight %, a melting point variation caused bya composition variation becomes smaller when the fusible alloy 13 isproduced. Therefore, it is possible to provide a thin-type thermal fusehaving a highly precise cut-off temperature by melting.

If the thermal fuse is used at a temperature exceeding the melting pointof the flux for a long time, it is necessary to set a high compositionratio for Zn as described above. In such a case, the composition ratioof Zn is preferably 2.0 to 5.0 weight %.

The flux to be coated on the fusible alloy 13 includes a resin obtainedby adding a wax component containing amide stearate and the like and byadding an activator to rosin. This flux promotes the surface tension ofthe fusible alloy 13 by the action of rosin in the flux to rapidly fusethe fusible alloy 13.

The melting point of the flux can be adjusted between about 50° C. andabout 120° C. by adjusting the added amount of the wax component. Sincethe flux cannot fulfil its function of promoting the surface tension ofthe fusible alloy 13 unless being melted, the melting point of the fluxis set to be lower than that of the fusible alloy 13 by adjusting theadded amount of the wax component. It should be noted that the meltingpoint of the flux is measured as a peak of a measurement result in ameasurement by a differential scanning calorimeter (DSC).

As the activator to be added to the flux may be preferably used: achloride activator for example, aniline hydrochloride, hydrazinehydrochloride, phenylhydrazine hydrochloride, tetrachloronaphthalene,methylhydrazine hydrochloride, methylamine hydrochloride, dimethylaminehydrochloride, ethylamine hydrochloride, diethylamine hydrochloride,butylamine hydrochloride, cyclohexylamine hydrochloride,diethylethanolamine hydrochloride, etc.; or a bromine activator forexample, aniline bromide, hydrazine bromide, phenylhydrazine bromide,cetylpyridine bromide, methylhydrazine bromide, methylamine bromide,dimethylamine bromide, ethylamine bromide, diethylamine bromide,butylamine bromide, cyclohexylamine bromide, diethylethanolaminebromide, etc.

The chloride activator has a higher reactivity with In and Zn than thebromine activator and quickly decreases in quantity. Thus, in the casethat the fusible alloy 13 includes the Sn—In—Zn alloy or Sn—Bi—In—Znalloy, the effect of the activator can be kept for a long time even whenthe thermal fuse is used at a temperature exceeding the melting point ofthe flux if the bromine activator is used.

It is preferable to add about 0.1 to 3% of the activator in order toenhance the activity of rosin. In such a case, if the thin-type thermalfuse is cut off by melting, for example., on a condition of increasingthe temperature by 1° C. per minute, the cut-off temperature by meltingis reduced by about 1° C. to 2° C. Thus, it is possible to provide athin-type thermal fuse having an excellent quick cut-off ability bymelting.

If the flux is melted, the activator reacts with the metals in thefusible alloy 13 to gradually decrease its quantity. Accordingly, if themelting point of the flux is set at 60° C. or higher, the activator inthe flux hardly decreases in quantity even if the thin-type thermal fuseis, for example, used in a packaged battery or the like at about 55° C.for a long time. Thus, it is possible to provide a thin-type thermalfuse having an excellent quick cut-off ability by melting.

Further, as shown in FIG. 1C, metal layers 16 including Sn, Cu or a likemetal having a good wettability to the fusible alloy 13 are provided onthe upper surfaces of the leading end portions of the metal terminals 12and connected with the fusible alloy 13. In this case, transportationsof the fusible alloy 13 toward the metal layers 16 after cut off bymelting are accelerated since the wettability of Sn or Cu constitutingthe metal layer 16 to the fusible alloy 13 is better than that of nickelconstituting the metal terminals 12. As a result, the fusible alloy 13can be quickly cut off after fusing.

Here, if S₁, S₂ denote an area of each metal layer 16 at the oppositesides along a direction perpendicular to the longitudinal direction ofthe fusible alloy 13 and an area thereof at the outer side of the end ofthe fusible alloy 13, the fusible alloy 13 is more quickly cut off as anamount of the melted fusible alloy 13 toward the areas S₂ increases.Therefore, a relationship of S₁, S₂ is set preferably to be S₁<S₂, morepreferably to be S₁<2S₂.

A single metal of Cu, Sn, Bi or In or an alloy of these metals may beused as a material for the metal layers 16. It is also preferable to usean, alloy having the same composition as the fusible alloy 13 as amaterial for the metal layers 16. In such a case, even if the metalconstituting the metal layers 16 diffuses into the fusible alloy 13, themelting point of the fusible alloy 13 does not change since thisdiffusion amount is tiny.

The thickness of the metal layers 16 is preferably 15 μm or smaller. Ifthe thickness exceeds 15 μm, a larger amount of the metal constitutingthe metal layers 16 diffuses into the fusible alloy 13, thereby changingthe melting point of the fusible alloy 13 to cause an operatingtemperature variation of the thermal fuse.

As described above, in this embodiment, the fusible alloy 13 forming thethermal fuse element located above the first insulating film 11 andconnected between the leading end portions of the pair of metalterminals 12 includes the Sn—In—Zn alloy containing: 45 to 55 weight %of In; and 0.5 to 5.0 weight % of Zn; with the balance being Sn or theSn—Bi—In—Zn alloy containing: 0.5 to 15 weight % of Bi; 45 to 55 weight% of In; and 0.5 to 5.0 weight % of Zn; with the balance being Sn. Thus,neither Pb nor Cd is contained in the fusible alloy unlike the priorart, with the result that a thin-type thermal fuse having no harm to thenatural environment can be provided.

Second Embodiment

FIGS. 2A and 2B show the construction of a thin-type thermal fuseaccording to a second embodiment of the present invention, wherein FIG.2A is a top view and FIG. 2B is a section along II-II of FIG. 2A. Thethin-type thermal fuse shown in FIG. 2 differs from the one shown inFIG. 1 in that a pair of metal terminals 2 a are formed to have a stripshape and projections 15 are provided at parts of the metal terminals 12a. Since other points are the same as in the thin-type thermal fuseshown in FIG. 1, no detailed description is given thereon.

As shown in FIGS. 2A and 2B, the round projections 15 are formed at endsof the metal terminals 12 a extending out from a first insulating film11 and a second insulating film 14. In this embodiment, effects similarto those of the first embodiment can be obtained. In addition, weldingstrength and welding positions can be stabilized to improve productivitysince a welding current can be concentrated if connection is made at theprojections 15 in the case that the pair of metal terminals 12 a andexternal wiring (not shown) are connected by electric welding.

Third Embodiment

FIGS. 3A to 3C are views showing the construction of a thin-type thermalfuse according to a third embodiment of the invention, wherein FIG. 3Ais a top view, FIG. 3B is a section along III-III of FIG. 3A, and FIG.3C is a top view partly in section corresponding to FIG. 3A.

The thin-type thermal fuse shown in FIG. 3 differs from the one shown inFIG. 1 in that a pair of metal terminals 12 b are attached to a firstinsulating film 11 a such that end portions thereof partly project fromthe lower surface of the first insulating film 11 toward the uppersurface thereof as shown in FIGS. 3B and 3C. Since other points are thesame as in the thin-type thermal fuse shown in FIG. 1, no detaileddescription is given thereon.

As shown in FIGS. 3B and 3C, an inner end portion of each metal terminal12 b is bent to have a substantially wavelike shape, thereby forming aprojection 15 a at a part of the end portion of the metal terminal 12 b,and the first insulating film 11 a is formed with notches 17 where therespective projections 15 a are to be mounted. By inserting theprojections 15 a into the notches 17, the pair of metal terminals 12 bare attached to the first insulating film 11 a such that the projections15 a thereof project from the first insulating film 11 a toward a secondinsulating film 14. A fusible alloy 13 is connected with the uppersurfaces of the projections 15 a. In this way, the fusible alloy 13forming a thermal fuse element is arranged between the first and secondinsulating films 11 a, 14 to be connected between the leading endportions of the pair of metal terminals 12 b.

As described above, in this embodiment, the positional relationship ofthe pair of metal terminals 12 b and the first insulating film 11 a canbe determined by engaging the projections 15 a with the notches 17.Thus, the pair of metal terminals 12 b can be precisely attached to thefirst insulating film 11 a and the thin-type thermal fuse can be highlyprecisely produced.

Further, in the thin-type thermal fuse of this embodiment as well, thefusible alloy 13 includes an Sn—In—Zn alloy containing: 45 to 55 weight% of In; and 0.5 to 5.0 weight % of Zn; with the balance being Sn or anSn—Bi—In—Zn alloy containing: 0.5 to 15 weight % of Bi; 45 to 55 weight% of In; and 0.5 to 5.0 weight % of Zn; with the balance being Snsimilar to the thin-type thermal fuse of the first embodiment. Thus,neither Pb nor Cd is contained in the fusible alloy unlike the priorart. As a result, it is possible to provide a thin-type thermal fusehaving no harm to the natural environment.

In this embodiment as well, the melting point of the flux applied to thefusible alloy 13 is set at 60° C. or higher similar to the firstembodiment. Thus, even if the thermal fuse is used at about 55° C. for along time, for example, by being used in a packaged battery, theactivator in the flux hardly decreases in quantity, wherefore athin-type thermal fuse having an excellent quick cut-off ability bymelting can be provided.

Similar to the first embodiment, metal layers 16 comprising Sn, Cu orthe like having a good wettability to the fusible alloy 13 are alsoprovided on the upper surfaces of the leading end portions of the metalterminals 12 b and are connected with the fusible alloy 13 as shown inFIG. 3C in this embodiment. In this case, since the wettability of Sn orCu constituting the metal layers 16 to the fusible alloy 13 is betterthan that of nickel constituting the metal terminals 12 b, thetransportation of the fusible alloy 13 after cut off by melting to themetal layers 16 is accelerated, with the result that the fusible alloy13 can be quickly cut off.

Similar to the first embodiment, the fusible alloy 13 is more quicklycut off as an amount of the melted fusible alloy 13 toward areas S₂increases in this embodiment if S₁, S₂ denote an area of each metallayer 16 at the opposite sides along a direction perpendicular to thelongitudinal direction of the fusible alloy 13 and an area thereof atthe outer side of the end of the fusible alloy 13. Therefore, it ispreferable to set a relationship of S₁, S₂ to be S₁<S₂, more preferablyto be S₁<2S₂.

FIG. 4 is a perspective view of a battery using an inventive thermalfuse. As shown in FIG. 4, a thermal fuse 22 is mounted on one sidesurface at a longer side of a battery main body 21. The thermal fuse 22is so electrically connected as to shut off a current upon the abnormalheat generation of the battery main body 21, so that the current is shutoff if the heat generated from the battery main body 21 reaches aspecified level or higher. Any of the above thin-type thermal fuses canbe used as the thermal fuse 22. Either a radial-type thermal fuse or anaxial-type thermal fuse to be described later may also be used. Anexternal electrode 23 of the battery main body 21 is provided on oneside surface at a shorter side of the battery main body 21, and oneterminal 25 of the thermal fuse 22 and the external electrode 23 areelectrically connected at a connecting portion 26 by means of spotwelding or the like.

Further, a protecting circuit 24 and the battery main body 21 areelectrically connected, and the protecting circuit 24 and an otherelectrode 27 of the thermal fuse 22 are electrically connected at aconnecting portion 28 by means of spot welding or the like. Parts of theprotecting circuit 24 are mounted on the protecting circuit 24 byPb-free solder such as Sn—Ag based solder or Sn—Cu based solder.

In the above battery, any of the thin-type thermal fuses according tothe first to third embodiments is used as the thermal fuse 22 and, inthis thin-type thermal fuse, the fusible alloy. 13 constituting thethermal fuse element includes an Sn—In—Zn alloy containing: 45 to 55weight % of In; and 0.5 to 5.0 weight % of Zn; with the balance being Snor an Sn—Bi—In—Zn alloy containing: 0.5 to 15 weight % of Bi; 45 to 55weight % of In; and 0.5 to 5.0 weight % of Zn; and a remainder of Snsimilar to the thin-type thermal fuse of the first embodiment. Thus,neither Pb nor Cd is contained in the fusible alloy unlike the priorart. As a result, it is possible to provide a thin-type thermal fusehaving no harm to the natural environment.

Further, in the above battery, any of the thin-type thermal fusesaccording to the first to third embodiments is used as the thermal fuse22 and, in these thin-type thermal fuses, the melting point of the fluxcoated on the fusible alloy 13 is set at 60° C. or higher. Thus, even ifthe thermal fuse is used at about 55° C. for a long time, for example,by being used in a packaged battery, the activator in the flux hardlydecreases in quantity, wherefore a thin-type thermal fuse having anexcellent quick cut-off ability by melting can be provided.

Fourth Embodiment

FIG. 5 is a section of a radial-type thermal fuse according to a fourthembodiment of the present invention. In FIG. 5, an insulating casing 31is in a form of: a cylindrical tube having a bottom formed and having anopening; or a rectangular tube having a bottom formed and having anopening, and comprising any of PBT (polybutylene terephthalate), PPS(polyphenyl sulphide), PET (polyethylene terephthalate), phenol resin,ceramic, glass and like materials.

The fusible alloy 32 is substantially in a form of a cylinder or arectangular column arranged in the insulating casing 31 and including anSn—In—Zn alloy or an Sn—Bi—In—Zn alloy. Thus, a radial-type thermal fusefree from Pb and Cd and having an operating temperature of 108° C. orlower can be provided.

The fusible alloy 32 preferably includes an Sn—In—Zn alloy containing:45 to 55 weight % of In; and 0.5 to 5.0 weight % of Zn; with the balancebeing Sn. In such a case, the melting point of the Sn—In—Zn alloy isabout 107° C., and a difference between a solidus temperature and aliquidus temperature becomes smaller to reduce a temperature range of asolid-liquid mixture. Thus, it is possible to provide a radial-typethermal fuse having a small operating temperature variation at about107° C.

Since the melting point can be decreased by adding Bi to the aboveSn—In—Zn alloy and reducing the content of Sn, the fusible alloy 32 mayinclude an Sn—Bi—In—Zn alloy containing: 0.5 to 15 weight % of Bi; 45 to55 weight % of In; and 0.5 to 5.0 weight % of Zn; with the balance beingSn. In such a case, it is possible to provide a radial-type thermal fusehaving an arbitrary operating temperature of 85° C. to 107° C.Specifically, if the content of Bi exceeds 15 weight %, the meltingpoint falls below 85° C. and the difference between the solidustemperature and the liquidus temperature becomes larger to increase anoperating temperature variation, wherefore a practical radial-typethermal fuse cannot be provided.

If the content of Zn exceeds 5.0 weight % in the above Sn—In—Zn alloy orSn—Bi—In—Zn alloy, the viscosity of the melted fusible alloy 32increases. Thus, a time required for the fusible alloy 32 to be cut offafter being melted is likely to vary. Therefore, the composition ratioof Zn is preferably 5.0 weight % or smaller.

Flux (not shown) including a resin obtained by adding a wax componentcontaining amide stearate and the like and by adding an activator torosin is coated around the fusible alloy 32. This flux acts to remove anoxide film of the fusible alloy 32 by being melted when the ambienttemperature increases. The flux also acts to promote the surface tensionof the fusible alloy 32 by the action of rosin in the flux to rapidly becut off the fusible alloy 13.

The melting point of the flux can be adjusted between about 50° C. andabout 120° C. by adjusting the added amount of the wax component. Sincethe flux cannot fulfil its function of promoting the surface tension ofthe fusible alloy 32 unless being melted, the melting point of the fluxis set to be lower than that of the fusible alloy 32 by adjusting theadded amount of the wax component. It should be noted that the meltingpoint of the flux is measured as a peak of a measurement result in ameasurement by a differential scanning calorimeter (DSC).

As the activator to be added to the flux may be preferably used: achloride activator for example, aniline hydrochloride, hydrazinehydrochloride, phenylhydrazine hydrochloride, tetrachloronaphthalene,methylhydrazine hydrochloride, methylamine hydrochloride, dimethylaminehydrochloride, ethylamine hydrochloride, diethylamine hydrochloride,butylamine hydrochloride, cyclohexylamine hydrochloride,diethylethanolamine hydrochloride, etc.; or a bromine activator forexample, aniline bromide, hydrazine bromide, phenylhydrazine bromide,cetylpyridine bromide, methylhydrazine bromide, methylamine bromide,dimethylamine bromide, ethylamine bromide, diethylamine bromide,butylamine bromide, cyclohexylamine bromide, diethylethanolaminebromide, etc.

The chloride activator has a higher reactivity with In and Zn than thebromine activator and quickly decreases in quantity. Thus, in the casethat the fusible alloy 32 includes the Sn—In—Zn alloy or Sn—Bi—In—Znalloy, the effect of the activator can be kept for a long time even whenthe radial-type thermal fuse is used at a temperature exceeding themelting point of the flux if the bromine activator is used.

It is preferable to add about 0.1 to 3% of the activator in order toenhance the active force of rosin. In such a case, if the radial-typethermal fuse is cut off by melting, for example, on a condition ofincreasing the temperature by 1° C. per minute, the cut-off temperatureby melting is reduced by about 1° C. to 2° C. Thus, it is possible toprovide a radial-type thermal fuse having an excellent quick cut-offability by melting.

If the flux is melted, the activator reacts with the metals in thefusible alloy 32 to gradually decrease its quantity. Accordingly, if themelting point of the flux is set at 60° C. or higher, the activator inthe flux hardly decreases in quantity even if the radial-type thermalfuse is, for example, used in a packaged battery or the like at about55° C. for a long time. Thus, it is possible to provide a radial-typethermal fuse having an excellent quick cut-off ability by melting.

If the flux is melted, the composition ratios of In and Zn may decreasesince, out of the metals constituting the fusible alloy 32, In and Znhave a higher reactivity with the flux than other metals. Thus, in thecase of using the thermal fuse at a temperature exceeding the meltingpoint of the flux for a long time, it is necessary to set highcomposition ratios for these metals. Therefore, in the above Sn—In—Znalloy or Sn—Bi—In—Zn alloy, it is preferable to set the content of In to48 to 55 weight % and that of Zn to 1.3 to 5.0 weight %.

Further, in the above Sn—In—Zn alloy or Sn—Bi—In—Zn alloy, the meltingpoint becomes quite stable for the composition ratio of Zn if thecomposition ratio of Zn is 1.3 to 5.0 weight %. Thus, if the compositionratio of Zn is 1.3 to 5.0 weight %, a melting point variation caused bya composition variation becomes smaller when the fusible alloy 32 isproduced. Therefore, it is possible to provide a radial-type thermalfuse having a highly precise cut-off temperature by melting.

If the thermal fuse is used at a temperature exceeding the melting pointof the flux for a long time, it is necessary to set a high compositionratio for Zn as described above. In such a case, the composition ratioof Zn is preferably 2.0 to 5.0 weight %.

One end portion of each lead conductor 33 is connected with acorresponding end portion of the fusible alloy 32, whereas the other endportion thereof is protruded through the opening of the insulatingcasing 31 to the outside of the insulating casing 31. The leadconductors 33 are wires comprising a single metal such as Cu, Fe or Nior an alloy of these metals, and metal plating of any one of Sn, Zn, Bi,In, Ag and Cu or an alloy containing these metals is applied to theouter surfaces of the lead conductors 33.

A sealing element 34 comprises a hard resin such as an epoxy or asilicone for sealing the opening of the insulating casing 31. Thefusible alloy 32 and a pair of lead conductors 33 can be connected bywelding or ultrasonic welding or by applying a power to the leadconductors 33 and the fusible alloy 32 to melt the fusible alloy 32.

As described above, in the radial-type thermal fuse of this embodiment,the fusible alloy 32 constituting the thermal fuse element includes anSn—In—Zn alloy containing: 45 to 55 weight % of In; and 0.5 to 5.0weight % of Zn; with the balance being Sn or an Sn—Bi—In—Zn alloycontaining: 0.5 to 15 weight % of Bi; 45 to 55 weight % of In; and 0.5to 5.0 weight % of Zn; with the balance being Sn. Thus, neither Pb norCd is contained in the fusible alloy unlike the prior art. Therefore, itis possible to provide a radial-type thermal fuse having no harm to thenatural environment. Further, since a pair of lead conductors 33connected with the fusible alloy 32 at one end portion are so protrudedthrough the opening of the insulating casing 31 outside the insulatingcasing 31 as to extend in parallel with each other, a degree of freedomin mounting this radial-type thermal fuse on a battery or the like canbe improved.

Fifth Embodiment

FIG. 6 is a section of an axial-type thermal fuse according to a fifthembodiment of the present invention. In FIG. 6, an insulating casing 41is in a form of a cylindrical tube having openings at opposite ends, andcomprises any of PBT (polybutylene terephthalate), PPS (polyphenylsulphide), PET (polyethylene terephthalate), phenol resin, ceramic,glass and like materials.

The fusible alloy 42 is substantially in a form of a cylinder or arectangular column arranged in the insulating casing 41 and including anSn—In—Zn alloy or an Sn—Bi—In—Zn alloy. Thus, an axial-type thermal fusefree from Pb and Cd and having an operating temperature of 108° C. orlower can be provided.

The fusible alloy 42 preferably includes an Sn—In—Zn alloy containing:45 to 55 weight % of In; and 0.5 to 5.0 weight % of Zn; with the balancebeing Sn. In such a case, the melting point of the Sn—In—Zn alloy isabout 107° C., and a difference between a solidus temperature and aliquidus temperature becomes smaller to reduce a temperature range of asolid-liquid mixture. Thus, it is possible to provide an axial-typethermal fuse having a small operating temperature variation at about107° C.

Since the melting point can be decreased by adding Bi to the aboveSn—In—Zn alloy and reducing the content of Sn, the fusible alloy 42 mayinclude an Sn—Bi—In—Zn alloy containing: 0.5 to 15 weight % of Bi; 45 to55 weight % of In; and 0.5 to 5.0 weight % of Zn; with the balance beingSn. In such a case, it is possible to provide an axial-type thermal fusehaving an arbitrary operating temperature of 85° C. to 107° C.Specifically, if the content of Bi exceeds 15 weight %, the meltingpoint falls below 85° C. and the difference between the solidustemperature and the liquidus temperature becomes larger to increase anoperating temperature variation, wherefore a practical axial-typethermal fuse cannot be provided.

If the content of Zn exceeds 5.0 weight % in the above Sn—In—Zn alloy orSn—Bi—In—Zn alloy, the viscosity of the melted fusible alloy 42increases. Thus, a time required for the fusible alloy 42 to be cut offafter being melted is likely to vary. Therefore, the composition ratioof Zn is preferably 5.0 weight % or smaller.

Flux (not shown) including a resin obtained by adding a wax componentcontaining amide stearate and the like and by adding an activator torosin is coated around the fusible alloy 42. This flux acts to remove anoxide film of the fusible alloy 42 by being melted when the ambienttemperature increases. The flux also acts to promote the surface tensionof the fusible alloy 42 by the action of rosin in the flux to rapidlyfuse the fusible alloy 13.

The melting point of the flux can be adjusted between about 50° C. andabout 120° C. by adjusting the added amount of the wax component. Sincethe flux cannot fulfil its function of promoting the surface tension ofthe fusible alloy 42 unless being melted, the melting point of the fluxis set to be lower than that of the fusible alloy 42 by adjusting theadded amount of the wax component. It should be noted that the meltingpoint of the flux is measured as a peak of a measurement result in ameasurement by a differential scanning calorimeter (DSC).

As the activator to be added to the flux may be preferably used: achloride activator for example, aniline hydrochloride, hydrazinehydrochloride, phenylhydrazine hydrochloride, tetrachloronaphthalene,methylhydrazine hydrochloride, methylamine hydrochloride, dimethylaminehydrochloride, ethylamine hydrochloride, diethylamine hydrochloride,butylamine hydrochloride, cyclohexylamine hydrochloride,diethylethanolamine hydrochloride, etc.; or a bromine activator forexample, aniline bromide, hydrazine bromide, phenylhydrazine bromide,cetylpyridine bromide, methylhydrazine bromide, methylamine bromide,dimethylamine bromide, ethylamine bromide, diethylamine bromide,butylamine bromide, cyclohexylamine bromide, diethylethanolaminebromide, etc.

The chloride activator has a higher reactivity with In and Zn than thebromine activator and quickly decreases in quantity. Thus, in the casethat the fusible alloy 42 includes the Sn—In—Zn alloy or Sn—Bi—In—Znalloy, the effect of the activator can be kept for a long time even whenthe axial-type thermal fuse is used at a temperature exceeding themelting point of the flux if the bromine activator is used.

It is preferable to add about 0.1 to 3% of the activator in order toenhance the activity of rosin. In such a case, if the axial-type thermalfuse is cut off by melting, for example, on a condition of increasingthe temperature by 1° C. per minute, the cut-off temperature by meltingis reduced by about 1° C. to 2° C. Thus, it is possible to provide anaxial-type thermal fuse having an excellent quick cut-off ability bymelting.

If the flux is melted, the activator reacts with the metals in thefusible alloy 42 to gradually decrease its quantity. Accordingly, if themelting point of the flux is set at 60° C. or higher, the activator inthe flux hardly decreases in quantity even if the axial-type thermalfuse is, for example, used in a packaged battery or the like at about55° C. for a long time. Thus, it is possible to provide a axial-typethermal fuse having an excellent quick cut-off ability by melting.

If the flux is melted, the composition ratios of In and Zn may decreasesince, out of the metals constituting the fusible alloy 42, In and Znhave a higher reactivity with the flux than other metals. Thus, in thecase of using the thermal fuse at a temperature exceeding the meltingpoint of the flux for a long time, it is necessary to set highcomposition ratios for these metals. Therefore, in the above Sn—In—Znalloy or Sn—Bi—In—Zn alloy, it is preferable to set the content of In to48 to 55 weight % and that of Zn to 1.3 to 5.0 weight %.

Further, in the above Sn—In—Zn alloy or Sn—Bi—In—Zn alloy, the meltingpoint becomes quite stable for the composition ratio of Zn if thecomposition ratio of Zn is 1.3 to 5.0 weight %. Thus, if the compositionratio of Zn is 1.3 to 5.0 weight %, a melting point variation caused bya composition variation becomes smaller when the fusible alloy 42 isproduced. Therefore, it is possible to provide an axial-type thermalfuse having a highly precise cut-off temperature by melting.

If the thermal fuse is used at a temperature exceeding the melting pointof the flux for a long time, it is necessary to set a high compositionratio for Zn as described above. In such a case, the composition ratioof Zn is preferably 2.0 to 5.0 weight %.

One end portion of each lead conductor 43 is connected with acorresponding end portion of the fusible alloy 42, whereas the other endportion thereof is protruded through the corresponding opening of theinsulating casing 41 to the outside of the insulating casing 41. Thelead conductors 43 are wires comprising a single metal such as Cu, Fe orNi or an alloy of these metals, and metal plating of any one of Sn, Zn,Bi, In, Ag and Cu or an alloy containing these metals is applied to theouter surfaces of the lead conductors 43.

Sealing elements 44 comprise a hard resin such as an epoxy or a siliconefor sealing the openings at the opposite ends of the insulating casing41. The fusible alloy 42 and a pair of lead conductors 43 can beconnected by welding or ultrasonic welding or by applying a power to thelead conductors 43 and the fusible alloy 42 to fuse the fusible alloy42.

As described above, in the axial-type thermal fuse of this embodiment,the fusible alloy 42 constituting the thermal fuse element includes anSn—In—Zn alloy containing: 45 to 55 weight % of In; and 0.5 to 5.0weight % of Zn; with the balance being Sn or an Sn—Bi—In—Zn alloycontaining: 0.5 to 15 weight % of Bi; 45 to 55 weight % of In; and 0.5to 5.0 weight % of Zn; with the balance being Sn. Thus, neither Pb norCd is contained in the fusible alloy unlike the prior art. Therefore, itis possible to provide an axial-type thermal fuse having no harm to thenatural environment. Further, since the insulating casing 41 in whichthe fusible alloy 42 is provided is in the form of a cylindrical tubehaving the openings at the opposite ends, there is no directionalityupon mounting this axial-type thermal-fuse on a battery or the like,wherefore the axial-type thermal fuse can be easily handled at the timeof production.

An electrical device to which the inventive thermal fuses are applied isnot particularly limited to the above battery, and the inventive thermalfuses are similarly applicable to other electrical devices to obtainsimilar effects. Further, characterizing portions of the respectiveembodiments can be arbitrarily combined. In such a case, the functionsand effects of the characterizing portions can be fulfilled.

INDUSTRIAL APPLICABILITY

As described above, since the thermal fuse element includes anSn—Bi—In—Zn alloy or an Sn—In—Zn alloy according to the presentinvention, neither Pb nor Cd is contained in the thermal fuse elementunlike the prior art. Thus, harm to the natural environment can besuppressed and the present invention can be suitably applied to athermal fuse element, a thermal fuse, a battery using such a thermalfuse, etc.

1-20. (canceled)
 21. A thermal fuse element being cut off by melting ata specified temperature, including either an Sn—Bi—In—Zn alloy or anSn—In—Zn alloy, wherein the alloys contain 45 to 55 weight % of In. 22.The thermal fuse element according to claim 21, wherein the thermal fuseelement includes an Sn—Bi—In—Zn alloy containing: 0.5 to 15 weight % ofBi; 45 to 55 weight % of In; and 0.5 to 5 weight % of Zn; with thebalance being Sn.
 23. The thermal fuse element according to claim 21,wherein the thermal fuse element includes an Sn—Bi—In—Zn alloycontaining: 0.5 to 15 weight % of Bi; 48 to 55 weight % of In; and 1.3to 5 weight % of Zn; with the balance being Sn.
 24. The thermal fuseelement according to claim 21, wherein the thermal fuse element includesan Sn—In—Zn alloy containing: 45 to 55 weight % of In; and 0.5 to 5weight % of Zn; with the balance being Sn.
 25. The thermal fuse elementaccording to claim 21, wherein the thermal fuse element includes anSn—In—Zn alloy containing: 48 to 55 weight % of In; and 1.3 to 5 weight% of Zn; with the balance being Sn.
 26. A thermal fuse comprising afusible alloy cut off by melting at a specified temperature, wherein thefusible alloy includes either an Sn—Bi—In—Zn alloy or an Sn—In—Zn alloy,wherein the fusible alloy contains 45 to 55 weight % of In.
 27. Thethermal fuse according to claim 26, wherein the fusible alloy includesan Sn—Bi—In—Zn alloy containing: 0.5 to 15 weight % of Bi; 45 to 55weight % of In; and 0.5 to 5 weight % of Zn; with the balance being Sn.28. The thermal fuse according to claim 26, wherein the fusible alloyincludes an Sn—Bi—In—Zn alloy containing: 0.5 to 15 weight % of Bi; 48to 55 weight % of In; and 1.3 to 5 weight % of Zn; with the balancebeing Sn.
 29. The thermal fuse according to claim 26, wherein thefusible alloy includes an Sn—In—Zn alloy containing: 45 to 55 weight %of In; and 0.5 to 5 weight % of Zn; with the balance being Sn.
 30. Thethermal fuse according to claim 26, wherein the fusible alloy includesan Sn—In—Zn alloy containing: 48 to 55 weight % of In; and 1.3 to 5weight % of Zn; with the balance being Sn.
 31. The thermal fuseaccording to claim 26, wherein the fusible alloy is coated by flux andthe melting point of the flux is 600 C or higher.
 32. The thermal fuseaccording to claim 26, wherein the fusible alloy is coated by flux and abromide activator is added in the flux.
 33. The thermal fuse accordingto claim 26, further comprising: a pair of metal terminals; a firstinsulating film to which the pair of metal terminals are attached; and asecond insulating film attached to the first insulating film so as todefine a space with the first insulating films, wherein the fusiblealloy is arranged between the first and second insulating films andconnected between the leading end portions of the pair of metalterminals.
 34. The thermal fuse according to claim 33, wherein La is setto lie within a range of 2.0 mm to 7.5 mm, wherein the La is a length ofa thermal-fuse main portion comprising the first insulating film, thesecond insulating film and the fusible alloy.
 35. The thermal fuseaccording to claim 33, wherein Lb is set to lie within a range of 0.4 mmto 1.5 mm, wherein the Lb is a thickness between the outer surface ofthe first insulating film and the outer surface of the second insulatingfilm.
 36. The thermal fuse according to claim 33, wherein a projectionis formed at an end portion of each metal terminal, the pair of metalterminals are attached to the first insulating film such that theprojections project from the first insulating film side toward thesecond insulating film side, and the fusible alloy is connected with theprojections.
 37. The thermal fuse according to claim 33, wherein aprojection is formed at an end portion of each metal terminal whichextends out from the first insulating film and from the secondinsulating film.
 38. The thermal fuse according to claim 26, furthercomprising: an insulating casing in a form of a tube having a bottomformed and having an opening; a pair of lead conductors whose each oneend portion protruded in the same direction through the opening of theinsulation casing outside the insulating casing; and a sealing elementfor sealing the opening of the insulating casing, wherein the fusiblealloy is placed in the insulating casing and connected with the otherend portions of the pair of lead conductors.
 39. The thermal fuseaccording to claim 26, further comprising: an insulating casing in aform of a cylindrical tube having openings at opposite ends; a pair oflead conductors whose each one end portion protruded through thecorresponding one of the openings at the opposite ends of the insulatingcasing; and sealing elements for sealing the openings at the oppositeends of the insulating casing, wherein the fusible alloy is placed inthe insulating casing and connected with the other ends of the pair oflead conductors.
 40. A battery, comprising: a battery main body; and athermal fuse electrically connected to shut off a current upon anabnormal heat generation of the battery main body, wherein the thermalfuse includes a fusible alloy which is cut off by melting at a specifiedtemperature, the fusible alloy includes either an Sn—Bi—In—Zn alloy oran Sn—In—Zn alloy, and the fusible alloy contains 45 to 55 weight % ofIn.